Gallium nitride (GaN)-based light emitting diodes (LEDs) have been broadly used in a wide range of applications including full color LED displays, LED traffic signboards, backlight units, lighting devices, and the like.
Generally, a GaN-based light emitting diode is formed by growing epitaxial layers on a substrate such as a sapphire substrate, and includes an n-type semiconductor layer, a p-type semiconductor layer and an active layer interposed therebetween. On the other hand, an N-electrode pad is formed on the n-type semiconductor layer and a P-electrode pad is formed on the p-type semiconductor layer. The light emitting diode is electrically connected to an external power source through the electrode pads and operated thereby. Here, electric current flows from the P-electrode pad to the N-electrode pad through the semiconductor layers.
On the other hand, a flip-chip type light emitting diode is used to prevent light loss by the P-electrode pad while improving heat dissipation efficiency. The flip-chip type light emitting diode emits light through a growth substrate and thus can reduce light loss by the P-electrode pad, as compared with a vertical type light emitting diode that emits light through epitaxial layers thereof. Furthermore, a lateral type light emitting diode is configured to discharge heat through a growth substrate such as a sapphire substrate and thus has low heat dissipation efficiency. On the contrary, the flip-chip type light emitting diode discharges heat through the electrode pads and thus has high heat dissipation efficiency.
Furthermore, a vertical type light emitting diode is fabricated by removing the growth substrate such as a sapphire substrate from epitaxial layers in order to improve light extraction efficiency. Particularly, the vertical type light emitting diode can prevent light loss due to total internal reflection by texturing an exposed surface of the semiconductor layer.
On the other hand, in a specific application, particularly, in an application requiring irradiation of light over a wide area as in a backlight unit or a sheet-lighting apparatus, a beam angle of light is an important issue.
Generally, a conventional flip-chip type light emitting diode has a beam angle of about 120°, and a typical vertical type light emitting diode has a smaller beam angle than about 120° due to surface texturing. Accordingly, in the related art, a molding member or a separate secondary lens is used in order to increase a beam angle of light at a package level.
On the other hand, a lighting apparatus such as an LED fluorescent lamp may require an LED having different beam angles according to directions. When a plurality of LEDs is mounted inside a lighting apparatus of an elongated fluorescent lamp shape, it is advantageous that the LEDs have large beam angles in a direction orthogonal to a longitudinal direction of the fluorescent lamp.